The Reconfiguration of the Stars

by Paul Gilster on February 20, 2008

Even the most adamant enthusiasts for METI — Messaging to Extraterrestrial Civilizations — haven’t come up with anything as audacious as what virtual reality guru Jaron Lanier is now talking about. Writing for Discover Magazine, Lanier has the notion of rearranging basic material objects to make them not just noticeable by aliens but blindingly obvious. Nothing new there, as the concept of such messaging goes back to the 19th Century. Mathematician Karl Gauss considered geometric plantings of trees and wheat to create shapes that might be visible from space, while Joseph von Littrow (perhaps basing the idea on Gauss’ work) talked about digging huge ditches and setting kerosene within them on fire at night, for the edification of beings on other worlds.

But Lanier isn’t talking about anything quite so mundane. This is a guy who thinks big — he wants to arrange stars. If you can find a way to create stable patterns of stars that are obviously artificial, then you have a celestial feature that shouts out your presence. Lanier calls such formations graphstellations, the idea being that we are creating an artificial constellation that is also a form of communication or writing. And perhaps other cultures, more advanced than ours, might have already chosen this path to tell us they’re out there.

As to why we might want to do this, Lanier simply accepts that making ourselves known is a good idea:

“Why move stars around? Because then they could be guided into orbital formations that almost certainly would not have occurred naturally. An imaginable set-up period of tens of thousands of years could therefore be leveraged into a much longer period—billions of years, perhaps—during which aliens could observe the fruits of our efforts.”

Judging from the reaction to NASA’s recent stunt — the transmission of a Beatles tune to Polaris — the idea of broadcasting the human presence seems to be settling in as a cultural trope. No one behind the NASA message seemed aware that there might be any controversy over the idea of beaming signals to the stars, and in the popular press the sending of the signal was handled more or less as a trendy cultural happening. Tau Zero journalist Larry Klaes has made the point here and elsewhere that we are soon to arrive at the juncture where individuals will have such powerful computing and transmission resources at their disposal that governmental or societal constraints on broadcasting will simply become moot. NASA’s latest has me wondering if he’s right. Like it or not, we may be moving into the era of METI as fait accompli.

Whatever the case, you have to admire the audacity of Lanier’s concept of star-moving. He imagines huge fleets of gravitational tractors gradually adjusting the trajectories of Kuiper Belt objects over thousands and thousands of years, eventually altering the Solar System’s trajectory through the Milky Way. In perhaps hundreds of thousands of years, our Sun can join up with other nearby stars similarly manipulated into the new graphstellation, a form of self-advertisement unrivaled by any other civilizational accomplishment in or out of Hollywood.

When Lanier took the idea to Piet Hut at the Institute for Advanced Study, the latter suggested a ‘multiply nested binary star graphstellation’ — a pair of a pair of a pair of double stars, sixteen stars in all. “An alien observer,” writes Lanier, “wouldn’t have to be able to discern all the individual stars in order to notice that something funny was going on; the alien would only have to note subtle changes in the qualities of the light, wobbles in the position, and other clues.”

So there you are. The long-term thinker’s brand of METI, played out over hundreds of thousands of years, and perhaps easier to construct than a Dyson sphere. Keeping our eyes open for such obviously artificial configurations would give SETI scientists yet another challenge, though whether any civilization would devote such time and energy into making itself into a cosmic beacon is questionable. Lanier makes me think of Olaf Stapledon, and engineering on cosmic scales of the sort that enlivened early science fiction. It’s a concept that plays against the apparently inexhaustible need of some humans to make our species known.

(hard): Gradually spin up a pulsar by ‘feeding’ it with angular momentum. Excellent galactic coverage and clearly unexpected behavior.

(easy): Space-based particle accelerator to stream light nuclei (artificial cosmic rays) at target systems, which can be digitally modulated. ETI can detect the message as the particles crash into their atmosphere.

Gradually spin up a pulsar by ‘feeding’ it with angular momentum. Excellent galactic coverage and clearly unexpected behavior.

Er, doesn’t that already happen in systems where the pulsar accretes from a binary companion? (Or perhaps you want to argue that millisecond pulsars are the remnants of previous METI attempts by other civilisations…)

As for doing interesting things to pulsars, the energy release from stuff falling onto the neutron star is huge. Anyone fancy dropping comets onto one at some interesting set of intervals?

(The yield from a white dwarf is rather less, but you don’t have to travel so far to get to one)

Another way to potentially contact or send signals to ETI would be to build thermonuclear devices with a mass of 10 EXP 15 metric tons or about 100 kilometers in diameter. Several such devices could be built and detonated at a safe distance from Earth in a binary digital signal patern to produce bursts of x-rays, gamma rays, and neutrinoes for the ETI to intercept.

The production of artificial white dwarfs out of the plane of the Milky way and then detonating them in an analogous manner is still another prospect although a very long term construction project. The material to form these stars could be gradually aggregated in super cool form to prevent the star from igniting fusion reactions. Some way of exhuasting compression induced thermal energy would be required.

Yet another more far out idea is to gradually construct a huge white dwarf densitied thermonuclear device with the mass of about 10 EXP 6 solar masses wherein the finished product would be a rotating toriod with a diameter of about 6 billion kilometers. The device could be gradually spun up until it reached the end of construction and a rotation velocity on the order of several hundred kilometers/second would prevent it from undergoing gravitational collapse before detonation. White dwarf dense toriodal material would allow for a thin aspect ratio toriod to reduce gravitational/rotational induced tidal forces which otherwise could tear the ring apart. A rotational velocity of say 500 km/second would permit the fusion energy yield to be effeiciently stored at about 5,000 times greater than that of the rotational kinetic energy.

This baby however would have to be constructed somehow far out of the galatic plane or far into intergalactic space, thus entailing a very long long constuction project. If such a device where detonated within the Milky Way Visible matter galaxy, the sterilization and complete extinction of all ETI civilizations within the Milky Way could result due to its lethal range of as great as 100,000 lighyears or 1000 times that of a carbon detonation supernova at perhaps 100 light years according to some models becuase of the inverse square drop off of radiation flux density. The plasma produced by the explosion might be recirculated via the galactic magnetic field thus enhancing lethality.

I can think of analogous systems made of matter/antimatter with a mass of 10 EXP 14 solar masses and a diameter on the order of lightyears, but such systems would be far to dangerous to construct. One such device could fatally irradiate the whole observable universe with its energetic gamma ray flux and so such devices are absolutely useless to consider for signalling purposes. In short, there is a practical peaceful limit to the size of such devices we would ever want to construct, but there is still room to broadcast a visible universe wide signal to our ETI brethren.

This is a subject that has had me thinking for a while. Really what we’re talking about is IMETI (Intergalactic METI) since any civilization that can influence the movement of stars on such a grand scale is likely to have had the means and the time to seek out other life in their own host galaxy.

But I would think there are better ways to be seen from across the cosmos. For starters, why not set off a cluster of supernovae at around the same time? Sure it would have to be somewhere out of the way of your home systems and given that most stars are several light years away from each other then no target galaxy would likely see them all go off at exactly the same time. Not to mention that the supernova light curve doesn’t remain that bright for all that long.

But… stars are hardly in short supply, so blowing up a few every few hundred years would probably not be a big deal, and if lined everything up with a target galaxy or a farther away cluster of galaxies and set off the stars in a discernible pattern (say four in square and a fifth one in the center for good measure) then even if they ended up being a couple of decades apart, a species with even our basic understanding of the universe would recognize that there was something unnatural going on in a galaxy far, far away.

Yeah, it would take millions of years for the message to be received, but if you’ve reached the point when you’ve explored your own galaxy and found that you’re alone, then assuming that death is less of a problem than it used to be (!) they may have nothing much better to do than sit around and wait.

And if you place a powerful enough radio transmitter next to the supernova pattern, then any civilization watching who recognizes the “We Are Here” signal can tune in and perhaps even be educated on how to communicate via, say (oh let our imaginations run wild) gravitons or some Star Trek particles that are not bound by the limit of the speed of light. (Perhaps that’s why it seems to be all quiet out there, they’re all talking to each other via a much faster and efficient means we haven’t even thought could exist yet).

While IMETI might be a little out of reach for, oh, the next few thousand years, ISETI is certainly something that’s worth considering. We can see an awful lont of galaxies and if life is really as rare as some people think, then may be some lonely species out there could be desperate enough to set something up for others to see.

Regarding what Ron and Andy said, modifying a pulsar’s timing or signal is certainly a good way to send a message a long distance, but again, I suspect that any civilization that can to that has already explored much of their own galaxy, either physically via robotic craft or by peering through a humongous array of telescopes.

So again, I suspect pulsars would be more useful in an IMETI (or should that be IGMETI?) and if you were able to modulate the timing of the pulses even a tiny amount then you could actually embed a full-blown message in the signal that could be picked up as an artifact of intelligence. But I don’t believe pulsars are all that detectable once you get much further away than Andromeda (correct me if I’m wrong) so what about using one of the standard candles that can be seen from much further away? i.e. Cepheid variables. The timing of the Cepheid pulses is not as regular as the millisecond timing of pulsars, but since astronomers of all species are likely to be looking for them as part of their work, they would be attractive subjects for embedding an IMETI signal in them somehow–perhaps altering the timing of the pulses or modifying the star’s spectrum in some way.

Maybe one day some astronomer will, by accident, see something odd and come across an IMETI signal. Given the number of galaxies we can see out there, I would not be very surprised if the first evidence of ETI came from outside rather than inside the Milky Way.

The concept of artificially arranged stars has appeared in at least one book that I can think of “The City and the Stars” (1956) by Arthur C. Clarke. It’s been a while since I read the book, but as I recall, a former Galatic Empire had formed several stars of different spectral types into a “Rosette” of (I think) seven stars that were so obvious that the protagonist (Alvin) headed there first when he was trying to figure out why mankind had abandoned the stars ages before.

Of course there was nothing in the book about HOW the Empire had managed to form the “Rosette”, but then there were a lot of bits of technology that were never explained either since there was nobody around to explain their workings to Alvin.

You’re right of course. I simply saw the radiation from infalling mass as a noisy by-product of adding angular momentum. The existence of stars that spin up naturally is something I knew about but assumed that by placing the mass source (even if one is intended to be detectable) too far out from the pulsar to explain the spinning up, to make it suspicious. I prefer your idea of parceling out the mass to encode a message.

In the next 100 years, we can expect to discover better ways to communicate that don’t involve using stars like graffiti spray paint. Patience, patience!

Artificial star formation is a pound foolish response to a penny priced challenge. It is far more likely that our first ET messages will come from improving our “seeing and listening” which might discover messages-that-are-there-right-now, then having to wait perhaps thousands of years for our engineering to enable such feats of advertising.

Proof: Fermi again. If star formation were the answer, we’d be seeing a lot of goofy-assed stuff out there right now with our present technology.

I don’t see anything Euclidish out there saying, “Gas and chow — easy on easy off — this exit.” If anyone sees such, please tele-order me a squirming bowl of gagh — the perfect food after traveling through a worm-hole!

I can only strongly agree with Edg Duveyoung: I do not like to use the word ‘stupid’ (especially not on this excellent website), but I can hardly avoid it here, with regard to the whole idea of rearranging stars for METI purposes.

Apart from the much discussed issue of the potential risk of attracting too much (in this case irreversable) cosmic attention (andy, where are you): as a means of doing so this represents an incredible overkill, like using atomic bombs for light houses.

Edg is right that the future is rather in improved and more sensitive ways of detection (and if we really want to, communication) than in wasteful and destructive mega-projects like this.

Certain things will probably never be done, not because an advanced civilization would not be able to, but because there will always be better ways to achieve the same goals.

Ronald says: “Certain things will probably never be done, not because an advanced civilization would not be able to, but because there will always be better ways to achieve the same goals.” Exactly my view as well, which is why I doubt any kind of SETI search will turn up this kind of artifact — surely there are less intensive ways of making the same declaration of existence.

Very advanced ETI might rearrange star systems for
maximizing resources in their region of space. Maybe
some globular star clusters are stars collected together
by an advanced ETI so they could have whole systems
of resources in one convenient location (hey, this is the
speculation thread, right?).

Or maybe they are doing it for aesthetic purposes,
essentially a work of art. When you live for ages, you
get tired of looking at the same old star patterns eon
after eon.

None of these ideas would have to be for signalling other
intelligences, except perhaps to say to less sophisticated
beings that they are one powerful species and should
not be messed with, because look what they can do
to the stars.

Personally I would be happy with a Dyson Shell or two.
Has anyone examined the galaxies to see if any of them
look “unusual” – maybe a second look at Halton Arp’s
Peculiar Galaxies.

@ljk:
“Very advanced ETI might rearrange star systems for
maximizing resources in their region of space”. It would be much (MUCH) more feasible, energetically and economically, to go to those stars and establish colonies there, instead of moving them (like moving the USA to Britain, by the pilgrim fathers).

Aesthetics and powerplay: OK, here you touch a topic which deals with the mind and culture, alsmost impossible to predict for alien intelligences.

Dyson shells (or rings): yes, possibly, because those would be very functional.

I think one of the most fundamental and ultimate criteria for any civilization to decide whether to do something, or rather to make a choice among alternatives, will be the expenditure in terms of time and energy.

Which is why I believe that Mars will (probably) be colonized in the foreseeable future (centuries), but Venus will (probably) not: the number of comet-like objects that need to be brought from the Kuiper Belt or Oort Cloud, in order to get enough water ánd speed up Venus’s rotation, will require so much energy (and time and effort and risk, …) that for much less ‘we’ can make it to Alpha Centauri. One escape: a civilization that can muster so much cheap energy that something like this could be done not for necessity or any functional reasons, but purely aesthetic ones, like a billionaire building a huge private park or zoo.

But necessity and functional requirement always come long before the luxury of (big) aesthetic projects, for any civilization. Which is why I believe that we, or any (other) advanced civilization will have colonized (significant parts of) the MW galaxy, long before we can even seriously consider any grand ‘restructuring projects’.

Ever see the animated series Invader Zim? One episode
dealt with the discovery that an ancient civilization on Mars
had turned the entire planet into a giant spaceship.

Why? Because it was a really, really cool thing to do.

There are plenty of practical reasons why moving stars
and their systems around is just too much effort. But a
really advanced society might do it just because it is a
really, really cool thing to do. Or as I said before, it is
a heck of a way to show just how powerful one is to the
rest of the neighborhood.

Stalin had a railroad built across Siberia. The Chinese
Emperor Qin Shi Huang had a Great Wall stretched across
the northern border of his realm for 4,000 miles. Both
cost a lot of money and resources and claimed many lives
in its construction. Why were they built? Essentially to show
how powerful their respective empires and rulers were to the
rest of the world.

So while I know even these structures pale in comparison to
something like rearranging stars, I note them to make a point
that just because something may not be practical does not
mean it won’t ever happen, thanks to the whims of whoever
is in control of the resources and economy. And don’t tell me
that even advanced beings won’t have their own motives for
power and survival. All living things are designed to survive,
no matter how simple or advanced they are. That is the
ultimate motivation of all life. Plus a habit of doing quirky,
illogical things every now and then.

For those who would like an idea of what a galaxy restructed
by an advanced ETI might look like, see this artwork by Jon
Lomberg:

This kind of METI attempt could send the message of “if you annoy us, we have the capability to lob stars at you“. Depending on how accurately you can do this, the effects could range from destabilising the planetary orbits to triggering mergebursts.

Similarly a Dyson sphere implies “we can disassemble planets at will”. Alastair Reynolds’ Galactic North has as its background Dyson-sphere-creation-as-weaponry…

Aliens would be alien so who knows what they might do. They might reconfigure the stars so as to send a message. Perhaps they never developed hearing, or a sense of touch, and would see visual signals as the only sure way of communicating. They might do it as a work of art. or religious purposes.

I myself think it more likely they would mine the stars for raw materials. The most massive star ever found has 114 solar masses, with a companion that has 84 solar masses. If a civilization capable of moving stars were to set up residence in such a system and mine the two stars they would have 198 solar masses to work with. How many space habitats would that build I wonder? Rather than taking over a few billion worlds and denying other species a foothold on them they might decide on a few trillion space habitats.

I also wonder what would happen to us if that 114 solar mass star goes supernova. Would 20,000 light year protect us. Any close neighbors of that system might want to hope that some species does come along and make use of it before that happens.

The theory of dark matter is that 85-90% of the mass in the universe is dark and does not interact with the electromagnetic force.

Recently there has been the design of metamaterials for magnetic shielding/invisibility Previously there has been work and designs for metamaterial to move microwaves, visible light and other wavelengths around a shielded region. There has also been recent progress on direct conversion of radiation into electricity and the highly efficient conversion of heat into electricity.

Scientists could use the metamaterial as a building block for a magnetic invisibility cloak. Such a cloak could hide magnetism by guiding an applied magnetic field around a cloaked region.

An advanced civilization could create a Dyson shell with metamaterials on the outside for guiding light, heat and magnetism around the shell [Dyson shell is converting all of the planets in a solar system into solar collecting satellites that orbit the star at about the distance of the earth. The structure lets you use all the solar energy of the star which would be over a trillion times more energy that our civilization uses]. Their shell would then have minimal interation with light and magnetism.

I had previous postings on the Fermi Paradox.

My speculation about technology and aliens is that we do not know what civilizations with technology able to explore the galaxy would be using. The Fermi paradox itself is based about speculations about aliens.

Some the Fermi speculation is on dyson spheres and dyson shells (visible megastructures) or visitations to our world. The megastructures might not be the easiest things to spot. They might look like some large infrared source about the size of earth’s orbit. Light would all be captured. Plus we are now learning how to convert heat to electricity in a very efficient way. A highly advanced civilization could be so efficient that they fade into the background of space.

We could be way off base trying to predict what a civilization hundreds, thousands or millions of years more technologically advanced than us would be doing.

Searches for extraterrestrial life usually involve trying to track down
unusual radio and optical signals. But could looking for “Dyson spheres” – artificial shells harnessing light from distant stars – be more productive?

Jim: Mind showing some math? I find it rather difficult to believe that anything could produce enough gamma radiation to destroy all life in the *universe.* Similarly I have doubts that a nuclear detonation on the order you suggested could sterilize the galaxy. What kinds of radiation tolerance thresholds are you thinking about (upper and lower bounds)? What equations are you using to derive the amount of energy discharged purely via gamma rays from a nuclear or M/AM detonation?

A toroidal thermonuclear device with a mass of mass of about 10 EXP 6 solar masses as I described above would have a yield of about 1 million carbon detonation supernova. The lethal radius of such supernova, although not know for sure, has been proposed to be on the order of a few dozen light years perhaps even greater according to some estimates. By the inverse square dependency of radiation flux intensity verses distance, the lethal radius could be (a few to several dozen Light-years)[( 10 EXP 6) EXP 1/2]. Since I am talking about a carbon detonation toroidal ring, the resulting radiation species should be very similar if not identical to that of a carbon detonation supernova.

For a matter/antimatter toroidal device with a mass of 10 EXP 14 solar masses and a diameter of about 60 lightyears, the yield would be equal to roughly 10 EXP 16 carbon detonation supernova with a potentially lethal radius of (a few to several dozen LYs)[(10 EXP 16) EXP 1/2] = (a few to several dozen light-years)(10 EXP 8) which is approximately equal to 4 billion to 10 billion light-years. Since the radiation from the detonation of such a matter/antimatter toroidal ring would continue at highly ionizing energies including hard gamma rays throughout every portion of the observable universe for a period of time at least equal to the light-transit time across the toroid divided by two, even locations as far away as the radius of the currently observable universe would be essentially bathed in lethal levels of gamma radiation as the radiation wave front passed through them for a period of about 30 years. Even red shifting of the radiation by a factor of 2 to 3 based on universe expansion at these locations would still leave the radiation well within the gamma ray band.

Actually, the radiation from either of the two devices described above would not consist of only pure gamma rays, but would include other particle species as well. A carbon detonation supernova might well bathe a planet such as Earth at a distance of as much as several dozen lighy-years with lethal levels of gamma rays for a time period on the order of years. Even though the Earth’s atmosphere may absorb virtually all incident gamma radiation, the atmospheric chemisty of the Earth’s atmosphere may be trashed in such a manner that the Earth’s biosphere would collapse ecologically in manners proposed by models of a nearby supernova explosion.

Since we have never experienced a supernova within a radius of a few to several dozen lightyears, we cannot really know what the effects of such an explosion would be on Earth’s biosphere.

A clever way to signal long distances would need some means of modulating the signal to carry information. Perhaps instead of hyper-bombs – as Jim described – we should be thinking of black-hole powered artificial nebula of some sort. A recent piece in “New Scientist” discussed “Black Hole Stars” which are accretion-powered masses with a large black-hole for a core. Such objects could be as luminous as a trillion suns – enough to be noticed across billions of light-years – and, assuming sufficient magnetic field deflection, possible to modulate the inflow into.

Without some tricky nuclear physics, not yet in evidence, it’s just not a reasonable proposition to make immense masses of antimatter, thus Eddington process accretion at 5.7% of mass-energy release is the most energetic process known. Thus big black-holes will remain the biggest and brightest things in the Universe.

The black hole powered artificial nebula is a fascinating idea. At a luminosity of a trillion suns, in one year, the black hole would output the equivalent of (3 x 10 EXP 7)(4 x 10 EXP 6)(10 EXP 12) metric tons of matter converted into energy. This is equal to 1.2 x 10 EXP 26 metric tons of mass converted to energy which is about an order of magnitude greater than the yield of a Carbon detonation supernova. Since the optical light frequency of a supernova waxes and wanes over a period of roughly a year as far as the majority of its brightest optical light output is concerned, I could well imagine as you stated above that a modulated beacon as such could be visible throughout the observable universe.

Regarding production of vast quantities of antimatter, unless we discover some ultra-efficient means of converted matter into antimatter, we will probably be consigned to producing only the quantities needed for interstellar space craft. Its hard to know for sure what future nuclear physics research will enable, but since the cost of the production of antimatter in even microscopic quantities is still very high, we might need to harness renewable energy sources such as solar energy or wind energy systems to produce modest quantities of antimatter. Perhaps space-based solar energy collectors could be used to power apparatus able to produce antimatter quantities necessary for interstellar manned relativistic space-craft.

Intensity of lasers is rapidly approaching the pair-production energy density needed for electron-positron pairs. Thus “positronium” held magnetically as Rydberg atoms, might “soon” be available for interplanetary rockets and early interstellar probes. Proton/anti-proton pairs will take a thousand-fold boost in laser intensity, which might be ~50-100 years after we make positronium. Thus efficiency of M/AM creation might rapidly improve in the not-too-far future.

If we can make it, can we store it? A severe problem with all antimatter creation is slowing the damn stuff down enough for it to form something more tractable, like a “cold plasma” or even anti-hydrogen ice. Perhaps some kind of dusty plasma is feasible? I don’t know. But it will be a real challenge if we want to pursue large masses of the stuff.

At 1% efficiency what would it cost to make? A kilogram of AM represents 50 billion kW.hr of embodied energy and 5 trillion kW.hr at our nominal efficiency. At $0.05/kW.hr that’s $250 billion. Quite an investment. How much bang for our buck do we get? One kg of antimatter can energise 1000 times its own mass of reaction mass to 0.063 c, enough to accelerate 200 kg to 0.1 c. Quite an expensive probe at $1.25 billion/kg.

But things might improve. For example, Focus Fusion Corp hopes to make power at a cost of $0.002/kW.hr. Thus a 25-fold improvement in antimatter price. That’s 5 tons of probe to 0.1c for the same investment of $250 billion – $50 million per kg. If power costs can be dragged down even further then matters improve manifold.

Actually I doubt an antimatter maker will be buying power. More likely dedicated facilities will be needed. To make 5 tons of the stuff in a reasonable time (~10 years say) we’d need 285 TW of power – 19 times total world power consumption. Could be a while before we get to that sort of power availability. Assuming we can find the requisite power sources then at 2.5% power growth we reach that level in ~ 2125. But that’s World total power. By 2300 that will have become just 1.25% of total power useage – presumably mostly off-world because the Earth’s heat budget would be massively perturbed by another 22 petawatts of heat needing dissipation. Assuming supply is massively cheaper than the present day, then that shouldn’t be too onerous a demand for a future space-agency.

BTW Interesting to compute the energy costs of getting to Mars at high-speed using the focus-fusion device for power. Assuming a 100 km/s mission delta-vee and ~ 0.5 efficiency then the energy cost to Mars is $8.70/kg. Assuming a ticket costs ~ 7 times that, then the price to get to Mars is ~ $4400 for a nominal 72 kg passenger. Not too bad. Akin to present day around-the-world tickets.

Thanks for the detailed mathematics. I still hope that at some distant future time, I most probably be long dead by then, we will learn how to produce copious amounts of antimatter.

But from your above detailed analysis, it sounds like we need to study efficient fusion rockets as a means to get to our nearby stellar neighbors during this century. Perhaps we can optimize the fusion energy to vehicle kinetic energy efficiency commensurate with an Isp of 4 million seconds. This would be pushing the limits of fusion energy conversion a bit, but every little bit of gain beyond an Isp of 2 million seconds dramatically improves terminal relativistic velocities. Magnetic sail or other breaking techniques could be used to slow the craft down so that minimal rocket thrusting would be necessary to slow the craft.

Heck, with all of the hydrogen available in the cosmos, we could perhaps build and launch world ships all over the observable universe and beyond given enough time.

I like the idea of fusion rockets and any workable ISR designs over beamed electromagnetic or kinetic energy because of the self contained nature of the former systems.

Fusion does have the advantage of potentially running on very abundant fuels – if we can run a CNO-cycle fusion reactor then our ships can burn straight hydrogen wherever it can be found. Early fusor craft might be pickier though – burning D-T, D-D, p-B, Li-Li, He3-He3, He3-D (roughly in that order of ease and energetics) – and these all require tricky extraction from the lesser Gas Giants.

The worst of all the fusion cycles is D-T because the Tritium has to be bred in a heavy lithium jacket. A D-T inertial confinement fusion design has been proposed for various interstellar missions with an expected ~ 900,000 s Isp. Acceleration is rather low because of the tritium requirements and the high neutron flux – equipment has to be shielded by BIG tanks of propellant.

Next up is D-D, which makes neutrons, but fewer than D-T. No lithium jacket needed, but the neutron flux is still challenging. Protium+Boron is next, lower energy, but all the products are charged particles. Likewise the others, with the most energetic being He3+D, though it produces some neutrons via D+D interactions.

Surprisingly CNO fusion isn’t as energetic in a useful way as it makes a lot of gamma-rays and neutrinos. But the fuel is everywhere.

By the way, I am curious about the process of so-called muon catalyzed fusion and how it might be applicable in manned interstellar space craft propulsion systems. My thought is that since muon catalyzed fusion is a rather low temperature fusion process, in some cases, not far removed from room temperature, perhaps such fusion energy might be used to drive steam driven turboelectric systems to power electron or ion rockets.

I am not sure what the rest mass to energy conversion efficiency of the highest mass specific energy yield muon catalyzed fusion reactions are, however, I believe that the muon catalyzed fusion results from a greatly reduced coloumbic barrier between the atoms undergoing fusion, thus the reason why the process can occur at temperatures close to room temperature. Muon catalyzed fusion is one so-called cold fusion mechanism that has had some serious consideration about 2-3 decades ago but I have not heard much more about it as of late.

I should probably search journals for further developments in this field in order to get the latest scoop on this concept.

I ran across an interesting research paper online in which a 5 stage fusion powered spacecraft could reach 0.64 C. Accordingly, the dry weight to total weight of each stage would be 0.1. The paper assumes no breaking, however, I believe that magnetic induction breaking, mag-sail breaking, or whatever could be used to slow the final stage down.

Assuming a first stage with a mass of 1 billion metric tons, the dry weight of the first stage would be 100 million tons. The second stage would have a mass of 100 million metric tons and a dry weight of 10 million metric tons. The third stage would have a mass of 10 million metric tons and a dry weight of 1 million tons and so one for a dry weight of 10,000 metric tons for the final stage including electro-dynamic breaking as I can envision it.

I can imagine 8 stages and much closer approach to C. The URL for this paper online is as follows;

If 0.64 C can be reached with fusion, imagine what we could do with a vehicle with a matter/antimatter fuel such as positronium with 5 stages wherein the dry weight to total weight of each stage is as above. Moreover, if the fuel was essentially pure antimatter in each stage for which the reactive matter was drawn from the interstellar medium, the effective efficiency of mass to energy conversion with respect to the ships reference frame would be 2[M(C EXP 2)]/[M(C EXP 2)] where M is the rest mass of the antimatter fuel. Talk about a rocket or jet engine on steroids.

If in the future, we find a form of mass wherein upon conversion of the mass into pure energy, E, is related by the following relation E = f(m)[M( C EXP 2 )] where f(m) >> greater than unity, a five stage rocket based on this fuel, the other parameters being the same would be awesome.

Abstract: Polaris, the nearest and brightest classical Cepheid, is a single-lined spectroscopic binary with an orbital period of 30 years. Using the High Resolution Channel of the Advanced Camera for Surveys onboard the Hubble Space Telescope (HST) at a wavelength of ~2255\AA, we have directly detected the faint companion at a separation of 0\farcs17. A second HST observation 1.04 yr later confirms orbital motion in a retrograde direction.

By combining our two measures with the spectroscopic orbit of Kamper and an analysis of the Hipparcos and FK5 proper motions by Wielen et al., we find a mass for Polaris Aa of 4.5^{+2.2}_{-1.4} M_\odot–the first purely dynamical mass determined for any Cepheid. For the faint companion Polaris Ab we find a dynamical mass of 1.26^{+0.14}_{-0.07} M_\odot, consistent with an inferred spectral type of F6 V and with the flux difference of 5.4 mag observed at 2255\AA. The magnitude difference at the V band is estimated to be 7.2 mag.

Continued HST observations will significantly reduce the mass errors, which are presently still too large to provide critical constraints on the roles of convective overshoot, mass loss, rotation, and opacities in the evolution of intermediate-mass stars.

Our astrometry, combined with two centuries of archival measurements, also confirms that the well-known, more distant (18″) visual companion, Polaris B, has a nearly common proper motion with that of the Aa,Ab pair. This is consistent with orbital motion in a long-period bound system. The ultraviolet brightness of Polaris B is in accordance with its known F3 V spectral type if it has the same distance as Polaris Aa,Ab.

Charter

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last nine years, this site has coordinated its efforts with the Tau Zero Foundation, and now serves as the Foundation's news forum. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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